About 90% of the soda ash (Na2CO3) production in the United States comes from the Trona deposits of Green River Basin in Wyoming. The trona (Na2CO3 NaHCO3.2H2O) is in the form of an ore of trona mixed with gangue material, which gangue material includes insoluble minerals and other undesired materials. A typical treatment process includes treating the ore by a direct process involving dissolution at high temperature, removing of sediments, and filtration for the removal of impurities, followed by subsequent crystallization and calcination for the recovery of soda ash. This method is known as the sesquicarbonate process. Other processes are also known, such as the monohydrate process, for example. Using this process, the trona ore can be calcined directly, followed by dissolution, purification, and crystallization to produce soda ash. In each of these methods, the operating costs can be higher than desired because selective mining must be practiced to minimize unwanted gangue minerals in the feed, and the chemical plant must be operated at a high temperature, thus increasing energy consumption.
A preferred processing strategy would be to remove insoluble gangue mineral contaminants from the plant feed to achieve a relatively pure trona product (a trona concentrate), which could then be further processed as desired, or even further marketed as a new trona product. Additionally, preprocessing at ambient temperature and pressure would reduce costs substantially by allowing for the use of less selective high capacity mining techniques, such as long wall mining. Still further, preprocessing can offer the possibility of generating a new product (trona concentrate), make available additional trona resources which are currently of marginal value, and result in improved operation of the chemical plant by providing high quality feed, thereby resulting in the ability to more readily achieve refined product specifications. Such a preprocessing strategy has been limited by the lack of satisfactory process technology.